The present invention relates to an ink jet recording head and an ink jet recorder of the type used to print an image by discharging ink drops from an electrode of the recording head and propelling them onto a recording medium.
An ink jet recorder discharges ink droplets from a discharge opening and guides them onto a recording medium. The dots are formed by leading ink from an ink tank to each discharge opening and applying kinetic energy to the ink, so that a small amount of ink in the form of a drop is discharged from a minute discharge opening, the ink drop is projected onto a recording medium, and an image is printed.
There is a method (electrostatic recording) of discharging ink by use of an electrostatic force, in which a voltage is applied between a common electrode, which is placed in contact with the recording medium, and a recording electrode, and this is one of the driving methods by which kinetic energy is applied to the ink. This method is recognized as a way to achieve high definition in an ink jet printer, because the amount of ink discharged on recording medium can be controlled by pulse-width-modulating the voltage applied to the recording electrode.
An example of such a method is disclosed in the Patent Application Laid-open No.7-502218 (PCT), in which ink, in which a coloring material is dissolved in a solvent in a low concentration, is supplied to the surface of the recording electrode, an electric field is formed by applying a voltage to the recording electrode, the coloring material subjected to the electric charge is agglutinated, and the agglutinated coloring material is discharged from the recording electrode on a path toward the recording medium. Further, the technology concerning the structure of the recording head in a recording method similar to the above-mentioned example is described in the Japanese Patent Application Laid-Open No. 11-34338.
An image is recorded by discharging agglutinated coloring material onto a recording medium by applying an electrical bias to the recording electrode, while making the ink circulate, collecting the ink in which the coloring material is agglutinated on the point of the recording electrode, and superimposing a pulse voltage on the electrical bias of the recording electrode in this state, thereby effecting electrostatic recording as disclosed in the above-mentioned official report.
Further, clogging of the ink is not generated easily in general in electrostatic recording because a small hole does not exist in the ink discharge part. Therefore, even if the recording head is manufactured in the form of a line head, a defective portion where discharge is not performed is not generated easily. Therefore, an ink jet recorder which has a line head can be achieved. There is a feature that it is possible to print at high speed because the record recorder with a line head can record on the recording medium at the same time in the omnidirection of width. However, because it is necessary to discharge the coloring material agglutinated at the point of the recording electrode in the method disclosed in the above-mentioned official report, it is necessary to supply a large amount of coloring material to print at high speed using high-speed ink circulation. Further, there is a limitation in making ink circulate at high speed in the flight channel (Hereafter simply called the channel) formed by micro-fabrication. Further, it is necessary to manufacture a lot of channels without a defect to achieve a line head. Further, it is necessary to have the same print characteristic in the press by all channels. Therefore, it becomes important to arrange the shape of a lot of the channels when a line head is manufactured, and to manufacture it cheaply and easily.
Further, when the interval of the recording electrode narrows, the discharge is influenced easily by the electric field generated by the voltage applied to the adjacent recording electrode in this recording method. There is also the displacement of the impact position of the discharge as a problem which occurs due to the influence of this electric field. The cause of this problem will be explained as follows.
The voltage applied to recording electrodes A and B, when a discharge is to be produced from the recording electrodes A and B and is not to be produced from an electrode C among three recording electrodes A, B, and C, increases more than the voltage applied to recording electrode C. Therefore, the component of the electric field directed to the recording electrode C is generated in the electric field in the vicinity of the point of recording electrode B. Therefore, the discharge produced from recording electrode B is impacted so as to approach the position on the recording medium where recoding is to be effected by recording electrode C. As a result, a problem of distortion of the image on the recording medium and a deterioration of the picture quality occurs. To prevent the potential applied to a recording electrode from being transferred to an adjacent recording electrode through the ink, the ink is divided into parts in each channel by providing a member for partitioning ink between recording electrodes arranged in a line. Therefore, not enough effect is achieved, though the displacement of the impact position of the discharge is reduced. Because the configuration disclosed in Patent Application Laid-Open No. 7-502218 (PCT) does not have a partition between recording electrodes arranged in a line, the displacement of the impact position of the discharge increases easily, when printing.
Further, each channel is divided by a partition, and the recording electrode is arranged at the position which comes in contact with ink which flows in the channel in the configuration disclosed the above-mentioned Japanese Patent Application Laid-Open No. 11-34338. Therefore, not enough effect is achieved, though the displacement of the impact position of the discharge is reduced.
Further, the recording head described in the above-mentioned official report has a relief structure formed from the ink channel bottom and the wall which partitions each ink channel. Therefore, costs of manufacture are high because the relief structure needs to be manufactured by using either a method of bonding with accumulating a concave part and a convex part or a method of cutting down the concave part using a dicer, etc.
Further, the recording head described in the above-mentioned official report does not have means to optimize the curve profile of the liquid level of ink (hereafter called an ink meniscus) due to the surface tension of the ink generated on the point of said recording electrode, which influences the concentration of the electric field on the point of the recording electrode of each channel. Because the concentration of the electric field on the point of the recording electrode is weak, it is necessary to raise the voltage applied to the recording electrode for effecting a discharge. As a result, the driving circuit for applying the voltage becomes expensive and the amount of flight of the discharge does not becomes uniform.
The present invention is directed toward solving the above-mentioned problems.
An object of the present invention is to provide an ink jet recording head which can prevent the impact position of the discharge from shifting and obtain a high definition image.
Another object of the present invention is to provide an ink jet recording head in which the shape of a lot of channels can be easily made uniform when line heads are manufactured, and which can be manufactured cheaply and easily.
Another object of the present invention is to provide an ink jet recording head which can be driven at a low voltage and in which the amount of discharge of ink can be made uniform.
Another object of the present invention is to provide an ink jet recording head which can print at high speed.
In accordance with the present invention, an ink jet recording head has a substrate, a plurality of recording electrodes arranged on said substrate, a plurality of control electrodes arranged so as to sandwich each of said recording electrodes, and an ink circulation part for supplying ink, which contains coloring material in a solvent, to said recording electrodes, to cause it to flow in a direction of the length of said recording electrode, and for collecting said ink from the point of said recording electrode.
The electric potential applied to the recording electrode of the channel from which ink is discharged is prevented from being shifted to a surrounding channel by individually providing ink channel for every channel through which ink passes. As a result, the electric field distribution around the recording electrode in the channel from which ink is discharged is stabilized, and the direction of ink discharge is stabilized. Further, the electric field distribution at the point of the recording electrode from which ink is discharged is stabilized and the direction of the ink discharge is stabilized by setting up control electrodes so as to sandwich the recording electrode and by applying constant potential to the control electrodes.
Further, an electrical discharge due to the electric breakdown of air is prevented by applying a protection film on the recording electrode.
Further, the ambient air along with ink from the recording electrode to ink collection channel is collected. The ink meniscus form is controlled by the collected air flow, and a low voltage drive and a uniform ink flight amount are made possible.
Further, the ratio of the insoluble material, such as the coloring material contained in the discharged ink is made lower than the ratio of the solvent, and printing speed is increased.